1. Field of the Invention
The invention relates to plane, hollow, reinforced concrete floors with two-dimensional structure and span in arbitrary direction. The present floor structure is part of a complete construction system developed for obtaining increased flexibility and a large beamless span.
2. Background Art
The weakness of concrete floor structures is considered well-known. Concrete floor structures have one fault. The dead load is usually 2-4 times heavier than the useful load capacity. This situation has resulted in numerous attempts being made to make the construction less heavy, mostly by forming various types of kind of internal cavities. Yet, no one has ever succeeded in finding a general solution to the problem. In order to obtain a practical solution, a large number of conflicting conditions necessarily have to be fulfilled. All previous attempts have been directed to the simple "one-dimensional" structure (span in one direction) rather than to the much more complex "two-dimensional" structure (span in arbitrary direction). The two constructions have quite different static functions and cannot be compared.
Since the 1950's, floors with one-dimensional structure have been fully developed by means of the prefabricated and prestressed hollow concrete element, where the hollow profile is made by monolithic concreting around steel pipes, which are drawn out of the element after cementation leaving cylindrical cavities in the concrete. The floor achieves maximum bearing strength corresponding to the concrete volume. However, the floor construction can only be made as a prefabricated element, and the load capacity exists only in one direction. This shortcoming impedes the whole building structure, as the construction has to be adapted to the floor elements to a large extent. The building system suffers from the necessity of bearing walls or beams and offers no true flexibility.
DE 2.116.479 (Hans Nyffeler April 1970) discloses the use of balls of lightweight materials instead of the mentioned pipes, whereby shortening of prefabricated pipes on the site may be avoided. In order to form a row of balls, the ball are provided with a through-going, central bore and threaded on a bar. The bars with the balls are supported by the reinforcement by means of chairs.
This idea has several drawbacks, which make it quite unrealistic. For instance the hollow balls within the bore will be surrounded by concrete, whereby the method is extraordinarily difficult to carry out in practice. Consequently, it can be concluded that the idea is possible in theory, but is in no way realistic. In connection with two-dimensional structures, the idea cannot be implemented at all. It would be completely impossible to thread balls on crossed bars.
Floors with a two-dimensional structure cannot be used rationally in conventional solid designs, especially in combination with supporting columns, because of the high weight/thickness ratio.
Without the use of columns, the application of a solid floor is restricted to small elements with a side length of about 3 to 5 meters, whereby the whole building structure is restricted to a very small structural module, thus this system also has a very limited flexibility.
No technique known from one-dimensional, hollow structures can be transferred to a two-dimensional, hollow structure.